Project Summary/Abstract This competing renewal of our longitudinal project proposes to elucidate mechanisms driving the initiation and progression of substance use is consistent with NIDA and NIMH's recently outlined strategic plans (NIDA, 2016; NIH CRAN, 2015; NIMH, 2015) prioritizing research on the period between adolescence and young adulthood. Defining features of typical adolescent development are increases in sensation seeking followed by more gradual increases in impulse control (described by the Dual Systems model). The discrepancy between developing sensation seeking and impulse control are theorized to result in risk-taking behaviors like substance use. In at-risk youth, these developmental processes may be further discrepant, which may be one mechanism for increased rates and severity of substance use involvement. The renewal project has been documenting the relationship of sensation seeking and impulse control since before substance use onset (10 to 12 years old at study entry), and this renewal will to continue to assess these processes and outcomes into young adulthood. More specifically, we will continue longitudinal assessments (every 6 months) of our at-risk (due to family history of substance use disorder) and control youth to monitor changes in substance use, impulse control, environmental, sensation seeking, risk and resiliency factors. Outcomes will be interpreted from the perspective of the Dual Systems model, and importantly, this work will extend this model by testing: (1) whether impulse control and sensation seeking develop independently from one another; (2) whether impulse control and sensation seeking development has additive or interactive effects on substance use involvement; (3) how the onset and escalation of substance use affects subsequent development of impulse control and sensation seeking; (4) how processes identified in the Dual Systems model develop among adolescents and young adults with family history risk; and (5) how social and environmental factors influence risk and resiliency for substance use and are interpreted in the context of the Dual Systems model. Interpreting these findings within the context of the Dual Systems model will help to refine and extend the key premises of this model, as well as reveal more detail about developmental mechanisms of substance use involvement.